Gramophone record



Nov. 22, 1938. E. SEVERIN ET AL 2,137,510

GRAMOPHONE RECORD Filed Aug. 6, 1936 Fig. I

Edwin fieverz'n Patented Nov. 22, 1938 UNITED STATES PATENT OFFICE many, I88

ignore to Telefu'nken Gesellschaft fiir Drahtlose Telegraphic m. b. IL, Berlin, Germany, a corporation of Germany Application August 6, 1936, Serial No. 94,509

In Germany August 16, 1935 Claims.

The invention relates to gramophone records, its object being the production of long-playing records.

The gramophone records hitherto usually made, which generally turn at a speed of 78 revolutions per minute, have playing duration of about 4 minutes with a groovewidth of ISO-180a, or microns, a. maximum amplitude of 60p. and a diameter of 30 cm. By reducing the speed of in rotation of the discs to one half or more, say 33 revolutions per minute, the playing duration of the records may be increased by somewhat more than double the duration. The introduction of such discs, however, is prevented by the fact that most driving devices have a speed of '78 revolutions per minute and can only be adapted for use with discs having a low number of revolutions by re-buildlng or interposition of special intermediate gears.

Furthermore, records having 33% revolutions per minute, if they are to have the same maximum amplitudes as records with '78 revolutions per minute, must be cut with a stylus the angle of relief (Hinterschlifiwinkel) of which may be very small owing to the steep rise of the groove with respect to the direction of movement, so that the production of the styli or even of the discs would give rise to great difficulties owing to the short life of the styli. Furthermore, in the playing of the records with such steeply cut maximum amplitudes difllculties arise, such as jamming of the needle, destruction of the record and the like.

It is therefore advantageous also to out long-- playing records preferably with a normal speed of 78 revolutions per minute. Now, in order that the diameter of the disc need not be increased and an extension of the playing duration may be obtained with the normal dimensions of ordinary commercial records, the hitherto usual precautionary measure of leaving a ridge between two oppositely lying maximum amplitudes has been dispensed with. It has hitherto been assumed that this ridge is absolutely essential for a safe guiding of the reproducing needle in the case of greater amplitudes.

In the hitherto usual cutting processes, it was possible for a partial intersection of the groove to occur during the recording even with a ridge width of 110;:- and a maximum amplitude of 60;. In this case, the recording was always repeated, as the probability of the maximum amplitudes again lying on the same point of the discs during the second recording was very small. The amplitudes were generally so far displaced with respect to one another, in relation to the direction of movement of the disc, that a cutting through of the ridge or an intersection of the grooves in the second recording did not occur. The ridge was thus always present between two 5 grooves in this case.

According to the invention, in a gramophone record with lateral recording the ridge generally lying between two grooves is cut away in the case of a maximum amplitude having to be cut so 10 that the grooves abut against one. another or partially intersect each other. Particularly when using pick-ups of small weight and small moment of inertia of the moved mass, which have no resonances, such as the rattle" resonances is occurring. in the hitherto usual pick-ups, in the transmission frequency range, it has been found that in the case of maximum amplitudes the pick-up is still safely guided on a record according to the invention. It has even been found 20 that when the sound track has an exceptionally great amplitude, so that it extends into the adjacent groove, a secure guiding of the reproducing needle in the sound track may nevertheless be obtained, so that sliding over of the reproducing 25 needle into the preceding track or into the adjacent grooves does not take place.

In order to lengthen the playing duration, the dimensions of the grooves may be altered according to a further feature of the invention. The 30 width of the grooves and the width of the ridge lying between two grooves (in the case of an empty groove) are, according to the invention, each reduced to about iii-50 the pitch or spacing of the grooves amounting to about 80-100 35 In the case of the records of the hitherto usual type, the width of the groove amounts to about 160-180 ,'and the ridge between two grooves to 110 vIf required, the width of the grooves and of the ridges may be further reduced. The depth 40 of the groove amounts only to about 2511. as compared with about 85,; in the hitherto known records. Moreover, the usual maximum amplitude of with about 200 cycles per second is reduced to approximately 30-35 with 200 cycles 45 per second, it having been found advantageous to make the groove width approximately equal to the maximum useful amplitude. It is now also possible with half the usual maximum amplitude to reduce the speed to about 33%; revolu- 60 tions per minute, so that the same cutting and reproducing conditions in relation to the angle of relief are obtained as with the records turning at 78 revolutions per minute of the type hitherto usually employed. The rise of the groove then lies approximately within the order of magnitude of the rise of the known records with '78 revolutions per minute. a

Furthermore, the cutting profile in the case of a long-playing record according to the invention is altered. Instead of the front angle of about 90 hitherto employed, a front angle of about 45 is adopted, in order that with the aforesaid groove width a suflicient groove depth may be obtained, which is necessary owing to the unavoidable striking of the wax disc. By means of these steps, it has been possible to effect an increase of the playing duration from about 4 minutes to about minutes at '78 revolutions per minute and *about minutes at 33% revolutions per minute.

In the accompanying drawing or diagram, Figure 1 represents a section through one of the hitherto usual gramophone records, while Figure 2 is a section through a record according to 0 the invention. Only a part of the records, on which the sound grooves. are recorded laterally, is shown in diagrammatic form. In the case of the record l,'on which sound grooves, in this case idle running sound grooves, are only shown on one side, the average groove width 3 amounts to about 160-180; while the ridge 4 between two grooves is approximately 1101:. The depth 5 of the grooves amounts to about 85 1.

3 playing record 6, in which, as is shown on the left-hand side, the average groove width I amounts to about 40-50 The ridge width 8 also amounts to about 40-50;. Either the modulated grooves may abut against one another, as shown in the centre of the figure, or the grooves may even intersect each other at the upper edges, as will be seen at the right-hand side, so that in the case of a maximum amplitude on the upper surface no complete ridge is present. The depth 9 of the grooves amounts to about 25;. While in the production of gramophone records in the manner hitherto usual the front angle I 0 amounted to 90, in the new form it amounts only to about 5 It will be seen from that description that the optimum playing duration is brought iabout by the combination of the individual elements of the invention, but that the individual elements per se also constitute a considerable advance.

What is claimed is: V

1. A gramophone record comprising a disk having a spiral acoustic groove of the lateral undulatory type, the width of the groove being approximately equal to its maximum amplitude, and the pitch of the groove being sorelated to the groove width and amplitude that adjacent groove' Figure 2 shows the groove profile for a long-.

vsections intersect each other at points where they are modulated maximum amplitude.

to at least two-thirds their 2. A gramophone record comprising a disk having a spiral acoustic groove of the lateral undulatory type, in which the maximum amplitude of undulation is at least approximately as great as the groove width, and in which the pitch, groove width, and maximum am plitude bear such a relation to each other that the contour of the record material between adjacent groove sections varies from that of a flat topped ridge to that of an inverted V the altitude of which at any point depends on the sum of the modulation amplitudes or the adjacent groove sections at such point.

3. A gramophone record comprising record material containing a spiral groove of constant pitch and width, said groove being laterally undulated due to sound, the

roove width and maximum ampiitude of undulation being approximately equal and being so related to the pitch that the pitch minus the width is at least as great as the maximum amplitude and is at most 1.7 times the maximum amplitude.

4. A gramophone record of the lateral undulatory type comprising a flat disk'having a spiral groove on one face thereof and a ridge in- $0 to 50 microns, and the said groove being from 40 maximum amplitude of to 50 microns, whereby "at points where adjacent groove sections are modulated to as much as two-thirds of their maximum amplitude the normal flat top of the intervening ridge is entirely cut away and the grooves intersect each other.

' 5. A gramophone record of the lateral undulatory type comprising a flat disk having a spiral groove on one face thereof and a ridge intervening between adjacent has a flat-top at points modulated by less than a groove sections which where the grooves are predetermined amount and an inverted V-shaped top at points where the grooves are modulated by more than said predetermined amount, the width of said groove being from 40 to groove being from to having a maximum width the maximum amplitude from 40 to 50 microns.

50 microns, the pitch of said microns, said ridge of 40 to 50 microns, and of said groove being EDWIN snvanm. o'rro BRUNNERT. 

